The present invention relates to a bridge unit that connects a plurality of segments as components of a network and, more particularly, of the bridge unit designed to support a movable host moving between the aforementioned segments.
The bridge unit connecting one segment to another monitors a source address (hereinafter referred to as SA) of a frame flowing on the respective segments so that a host connected to those segments is recognized. The bridge unit realizes efficient frame transfer based on the above-obtained host location information.
Supposing that each segment of the network is constructed using a broadcast medium such as "Ethernet" proposed by Xerox (U.S.A.), rules of the frame transfer are specified as follows.
1: If a destination address (hereinafter referred to as DA) of a received frame is a broadcast address, the broadcast is executed to all segments except the reception segment that the received frame has been transmitted.
2: If a segment connecting the host defined by the DA of the received frame is identified and the identified segment does not coincide with the segment that the received frame has been transmitted, the received frame is transferred to the segment connecting the identified host.
3: If a segment connecting the host defined by the DA of the received frame is identified and the identified segment coincides with the segment that the received frame has been transmitted, the identified segment is able to receive the received frame at all nodes, thus abandoning the received frame that is not required to be transferred.
4: If a segment connecting the host defined by the DA of the received frame is not identified, the received frame is transferred to all segments except the segment that the received frame has been transmitted.
When the host transmits the frame while moving between segments, the bridge unit misjudges that the host is connected to a plurality of segments, resulting in misleading host location information. In order to solve the aforementioned problem, a bridge unit that detects a host movement by monitoring a frame flowing on the segment so as to immediately update the host location information is disclosed in JP-A-217141/1992 or JP-A-154335/1992.
In case of a plurality of segments each formed of a radio medium, the host may locate halfway between those segments. In such a case, the conventional art can no longer overcome the above-described problem.
As it is known that the radio transmission path varies with time, the frame transmitted from a certain segment cannot always be received. In order to realize stable communication, it is desirable to receive the respective signals on a plurality of segments simultaneously. Transmitting the frame on a plurality of segments simultaneously may stabilize the communication. However unnecessary traffic may be generated compared with transmission of the frame only to a single segment.